1. Field of the Invention
The present invention relates to a liquid crystal optical modulator such as a liquid crystal display or liquid crystal optical switch and to a process of producing the same, and more particularly to a seal for sealing the liquid crystal.
2. Description of the Related Art
A liquid crystal optical modulator such as a liquid crystal display or liquid crystal optical switch is formed, for example, by providing a liquid crystal layer between substrates comprising electrodes.
Usually, a liquid crystal cell is formed by bonding substrates disposed with a certain gap therebetween with a resin, injecting a liquid crystal through an injection port into the space bounded by the resin and the substrates, and sealing after the injection of the liquid crystal has been completed. In the above-described configuration in which a liquid crystal is held between the substrates with a resin, a problem is associated with the degradation of liquid crystal characteristics caused by permeation of moisture into the liquid crystal layer through the resin. Another problem is that a spacer is required to set the predetermined distance between the substrates, and yet another known problem is that deformations occur due to physical properties of the resin and a narrow seal width is difficult to realize.
As a configuration that increases a moisture resistance characteristic and strength characteristic, the inventors of the present invention suggested a double sealing structure in which the periphery of the liquid crystal is double sealed with a sealing material. Japanese Patent Application Laid-open No. 2006-267532 suggests a sealing configuration that can be used over a long period under high-temperature and high-humidity conditions, in which a linear expansion coefficient of a first sealing member on the side of the liquid crystal member is made less than a linear expansion coefficient of the second sealing member provided on the outside, and the hygroscopicity of the second sealing member is made less than the hygroscopicity of the first sealing member.
In addition to the aforementioned sealing structure in which the liquid crystal layer is held by a resin seal, structures in which the sealing portions are configured of a metal have also been suggested (for example Japanese Patent Applications Laid-open No. 49-46449 and 4-278983).
In the invention of Japanese Patent Application Laid-open No. 49-46449, thin films of a high-melting metal are provided on the surfaces of both substrates, a low-melting metal such as a solder is introduced between the thin films of a high-melting metal, and the substrates are joined together by fusing at a comparatively low temperature.
Further, in invention of Japanese Patent Application Laid-open No. 4-278983, a seal is configured by providing metal films such as Al films on the surfaces of both substrates and introducing a low-melting metal such as a solder between the metal films. After the two substrates have been stacked, sealing and joining are performed by spot heating the sealing portion and melting the low-melting metal. FIG. 22 is an example of sealing configuration in which a low-melting metal such as a solder is introduced between metal films. In a liquid crystal cell 101 shown in FIG. 22, a counter electrode 104 and a pixel electrode 105 are provided on respective surfaces of upper and lower substrates 102, 103, and the substrates 102, 103 are disposed opposite each other via a spacer 109 located therebetween so that the electrodes 104, 105 face each other.
A thin film 106 of a high-melting metal is provided via an insulating layer 110 on the counter electrode 104, and a thin film 107 of a high-melting metal is provided on the pixel electrode 105 in a position facing the thin film 106 of a high-melting metal. A low-melting metal 108 such as a solder is sandwiched between the thin film 106 of a high-melting metal and the thin film 107 of a high-melting metal. The thin film 106 of a high-melting metal and the thin film 107 of a high-melting metal are joined together by melting the low-melting metal 108.
The above-described configuration in which the seal is formed from a metal, the problem of moisture permeation into the liquid crystal layer through the sealed portion is resolved, but the configurations that have heretofore been suggested require metals of two types: a high-melting metal and a low melting metal. Furthermore, a low-melting metal has to be sandwiched between the thin films of high-melting metals on the surfaces of both substrates and, therefore, the production process is complex.
It is an object of the present invention to resolve the above-described problems and to perform sealing with a metal between substrates in a liquid crystal optical modulator with a simple configuration.